Gender roles are the associated behaviors, roles, expectations, etc., associated with being a man or a woman in society. There's nothing innately natural about what women do and what men do--as you grow up, you learn how men and women are supposed to act in our society. You learn the gender roles through socialization, then adopt them and internalize them yourself. You develop a picture of how males and females are supposed to act, and adjust your behavior accordingly.
These gender roles, as mentioned, are socially constructed. Each society constructs its own notion of gender roles, and as members of that society, people internalize and adapt them.
Just as gender roles change through time, they also vary from society to society. For instance, what it means to be a man and woman--the gender roles associated with those meanings--in Pakistan is not the same as what it means in the United States today.
Given constructions of gender socially, people organize power in society accordingly, along different gender lines. In the process, they establish matriarchy or patriarchy.
Throughout history, patriarchal societies have been more common, with matriarchy being far more rare. The abundance of patriarchal societies and the persistence of patriarchy in society helps to explain the existence of sexism.
Sexism is an ideology that holds that one sex, usually males, is inherently better than another. Sexism has social consequences, especially when it becomes institutionalized.
Currently, this state of affairs is changing--women are starting to fill out occupations that were typically male. This is somewhat mitigated through the passage of time and through gender equality, yet you still see sexism in society and continue to live in a patriarchal society.
In the same way that society constructs categories of gender, it also constructs meanings to other categories, like race, class, age, and sexual orientation. Intersectionality is a sociological theory that holds that multiple forms of disadvantage--or conversely, advantage--converge together to form an interlocking system of disadvantage (or advantage) for certain people or groups in society. Various identity categories combine or intersect into interlocking systems of advantage or disadvantage.
Being a very sociological idea, this idea provides a way to think about how different intersections of socially-constructed identity such as gender, race, class, and age combine and converge to structure a set of advantages or disadvantages in society, which in turn converge and structure people’s life chances. Intersectionality helps in understanding the connections between gender and other social identities in society.
Intersection is a kind of sociological ‘buzzword.” It’s very common for sociologist to profess studying, for example, the intersection of environmental politics and class, or the intersection of race and gender.
Source: This work is adapted from Sophia author Zach Lamb.